1. Field of the Invention
This invention relates to an improvement in segmented, transversely curved rolls for conveying glass sheets and particularly those that have just been heated to a temperature sufficient for shaping and tempering. The heated glass sheets sag by gravity during their delivery through a roll forming station to a cooling area where cold tempering medium is applied toward the opposite major surfaces of said sagged glass sheets at a rate of flow and pressure sufficient to impart at least a partial temper in the sagged glass sheets. This invention also may find use in providing, in the cooling area, additional curved rolls having a transverse curvature to which the sagged glass sheets conform while conveyed thereover.
When glass sheets are conveyed on a roller hearth through a tempering apparatus that includes a heating area, a shaping area and a cooling area in end to end relation to one another, it is important that the conveying rolls of the roller hearth be of a material capable of withstanding the heat in the area in which the rolls are installed and that do not mar the engaged surfaces of the conveyed glass sheets. It is also important to minimize the relative sliding between the moving hot glass sheets and the rotating curved rolls that convey the hot glass sheets. One method the prior art used to minimize relative sliding is to drive a series of identical conveyor rolls from a common drive so that all the rolls rotate at the same rotational speed.
In the heating area, superior rolls for conveying flat glass sheets by rotation until the sheets are heated sufficiently for shaping and tempering are composed of a sintered fused silica material that is made by grinding solid fused silica into small particles and then sintering these particles to each other at a temperature below the silica fusion temperature. Such a material is readily formed into an elongated cylindrical shape required for the rolls of a roller hearth conveyor. In addition, fused silica rolls so formed have a relatively small coefficient of thermal expansion. This latter characteristic is extremely desirable due to the extreme temperature range to which the rolls of the roller hearth in the heating area of the tempering apparatus are subjected during use.
Fused silica, closely spaced, conveyor rolls of cylindrical shape are suitable for conveying flat glass sheets. Likewise, closely spaced transversely shaped rolls provide suitable support for conveying curved glass sheets. However, glass sheets transported by a conveyor of widely spaced, fused silica rolls are free to sag out of their desired transverse shapes during their conveyance between adjacent of said widely spaced rolls, particularly in the hottest portion of the roller hearth conveyor. Hence, conveyor rolls should be capable of close spacing.
Furthermore, in the cooling area beyond the heating area, fused silica rolls having such desirable properties at the elevated temperatures of the heating area are overengineered for withstanding the milder temperatures that exist downstream of the heating area. Hence, it would be practical to use rolls suitable at lower glass engaging temperatures that are less expensive than the fused silica rolls that must be used in higher temperature atmospheres.
When glass sheets are shaped in a shaping area by roll forming, as in U.S. Pat. Nos. 3,701,644 to Robert G. Frank or as in 4,139,359 to Randall S. Johnson and Terry L. Wolfe, after being delivered to a roll forming station located downstream of the heating area where the roller hearth is located, or by press bending as in U.S. Pat. No. 4,015,968 to Robert G. Revells et al., for example, or by inertia sag bending as in U.S. Pat. No. 3,476,540 to George F. Ritter et al., and the curved glass sheets are supported on a roller conveyor for passage through a cooling area, the sheets must retain their shapes during their delivery through the cooling area. Also, the conveyor should have means to prevent the forming of scuff marks on the surfaces of the curved glass sheets during the passage through the cooling area.
The glass sheet tempering art would welcome relatively inexpensive and durable rolls for conveying curved glass sheets into and through the cooling area of a glass sheet tempering apparatus. The glass sheet shaping art would welcome less expensive, curved shaping rolls than the solid ceramic rolls disclosed in the heating areas of prior art roller hearth conveyors.
In addition to maintaining the shape of the curved glass sheets and avoiding the development of scuff marks in the shaping and/or cooling area, it is also desirable to have glass sheet conveyor rolls in the cooling area that occupy a minimum possible portion of the cooling area so as to provide minimum interference with the flow of cold tempering medium toward the opposite major surfaces of the curved glass sheets to be tempered. Curved segmented rolls have been developed for use in transporting glass sheets through shaping and/or cooling stations. These rolls include short segments having interfitting elements that transmit a torque from segment to segment. A spring provided to insure positive engagement of the interfitting elements causes the end segment against which it bears to drag during a portion of each rotational cycle and also may scratch the end segment to develop wear marks on its surface facing the spring. With a single common drive rotating a plurality of segmented rolls in unison at a given average rotational velocity, the portion of each rotational cycle subject to drag and the amount of drag usually differs from roll to roll. The roll rotation must accelerate from the drag portion of the rotational cycle to equalize the average rotational speed of each roll driven from a common drive shaft. The non-uniformity of rotational speed cycles of different rolls may cause surface marks on the conveyed glass sheets. It would be beneficial to eliminate or even reduce frictional drag and surface wear of the end segment due to the biasing spring.
2. Description of Patents of Interest
U.S. Pat. No. 1,156,386 to Armstrong discloses a belt idler comprising a bracket supporting a pair of upwardly inclined spindles with an idler pulley rotatably mounted about each of the spindles. The pulleys support the upper run of a V-shaped belt, which is supported on the idler pulleys. Each idler pulley rotates independently of the other idler pulley in response to friction from the moving belt. The belt would interfere with flow of tempering medium, so that this apparatus is not suitable to convey curved glass sheets through a cooling area of glass tempering apparatus.
U.S. Pat. No. 1,516,083 to Curtis discloses a roller conveyor comprising composite rolls of concave elevation. Each composite roll comprises five axles disposed in end to end relation, a roller on each axle, a hub for each roller, four supporting brackets (one for each joint) between adjacent hubs, and means to adjust the tightness between adjacent hubs. The bracket supports intermediate the ends of the composite rolls would inhibit the free flow and escape of tempering medium, if used to convey curved glass sheets through the cooling area of glass tempering apparatus.
U.S. Pat. No. 1,927,849 to Roberts discloses a cloth expander and guide that comprises a shaft device comprising companion shafts angularly related with their inner ends pivotally connected at the center of the shaft device. Such a device would not be suitable to convey curved glass sheets through the cooling area of glass tempering apparatus.
U.S. Pat. No. 2,828,852 to Lorig discloses a roller conveyor comprising certain self-centering rolls of special construction. The special rolls are mounted on a bent shaft and comprise a pair of generally frustoconical shaped rolls or cylindrical rolls with tapered ends of smaller diameter mounted on the shaft with the small diameter ends adjacent each other. The rolls are connected to rotate at the same angular velocity. However, these rolls are not suitable for apparatus to temper curved glass sheets.
U.S. Pat. No. 2,948,384 to Pate discloses a belt conveyor comprising a plurality of rolls. Each roll includes a plurality of idler rollers mounted in spaced relation along the length of a flexible cable. The latter is stationarily fixed at its ends to a conveyor support framework. The flexible cable is tubular and provided with lubricating fittings for maintaining adequate lubrication for bearing assemblies incorporated in the idler rollers. This apparatus is not suitable for glass tempering.
U.S. Pat. No. 3,213,513 to Robertson discloses a segmented curved roll in which the ends of adjacent segments mounted on a curved shaft are stepped or rabbeted to form tightly fitting, axially overlapping joints surrounding spools. The latter are received in axially spaced end to end relation along the curved shaft with annular spacer rings separating adjacent bearing races mounted along the shaft.
U.S. Pat. No. 3,308,519 to Westgate discloses a segmented curved roll with reinforcing rings that is similar in construction to that of the Robertson patent described in the previous paragraph.
U.S. Pat. No. 3,485,618 to Ritter discloses rolls for conveying glass sheets. Each roll has a resilient spring extending between a pair of rigid stub rolls and covered by a tubular sleeve of a soft, non-abrasive, resilient material such as fiber glass cloth. The spring and stub rolls are so dimensioned that a glass sheet rests partly on the stub rolls and partly on the resilient spring when flat and, when the glass sheet is bent, it rests exclusively on the spring.
U.S. Pat. No. 3,550,758 to Stalker discloses an idler roller for conveyor belts with special lubricating structure that includes spiral grooves formed in the sidewalls of each roller to help pressurize lubricant within the grooves when the roller rotates. This apparatus is also unsuitable for glass tempering.
U.S. Pat. No. 3,763,992 to Klenk discloses a conveyor of rollers that extend obliquely of a path of movement to force sheets transported thereover toward a guide at one side thereof. The obliquely extending rollers are driven by stub shafts that extend perpendicular to the path of movement through universal joints. A belt drives the stub shafts in unison. The obliquely extending rollers are of cylindrical shape and would not be suitable for use in conveying bent glass sheets.
U.S. Pat. No. 3,799,752 to Cheron discloses rolls having straight aligned end portions interconnected by arcuate portions. The rolls pivot about their end portions between an orientation where the arcuate portions lie in a horizontal plane to support flat glass sheets and other orientations angularly disposed to the horizontal in which the arcuate portions present arcuate elevations for rotatably supporting and conveying the glass sheets.
U.S. Pat. No. 3,871,855 to Frank discloses a segmented forming roll for roll forming apparatus that is provided with snap rings that act as low friction bearings to enable adjacent segments of the forming roll to rotate independently of one another at different rotational speeds. The different rotational speeds correspond to a desired more uniform peripheral speed among the rotating segments of different diameter that cooperate to form a transverse shape corresponding to one desired for glass sheets transported thereagainst during the roll forming operation.
U.S. Pat. No. 3,918,774 to Nicholson discloses bowed rolls for use in the paper or textile industries. The rolls comprise an elongated shaft, a series of spools disposed about the shaft for rotation and bearings between the shaft and the spools. Longitudinally split spacers separate adjacent bearings. Each spacer has its opposite ends tapered to abut against surfaces of the side walls of the inner races of said adjacent bearings that are complementarily tapered. There is no teaching of how this apparatus would be suitable to temper glass.
U.S. Pat. No. 3,961,737 to Fatula discloses a self-centering roll having two tubular end rim portions mounted on a straight shaft in spaced relation to one another. Means including a deflectable end web and an inner web including an eccentric hub, bearings mounted on the eccentric hub and a member eccentric with respect to the shaft axis mounted on the outside of the bearing concentric with the bearing axis cause the end rim portions to rotate on axes that intersect at a point intermediate the inner webs and are arranged at the same angle to the shaft axis. The roll of this patent is not curved to conform to the transverse shape of conveyed glass sheets.
U.S. Pat. No. 4,033,497 to Przygocki discloses a segmented billet roll provided with removable and axially adjustable segments having tongue and groove connections that interfit with one another and may be adjusted along the length of a central shaft to lengthen or shorten the length of the billet roll to accommodate for sheets of different widths. Set screws are provided to lock the position of each segment along the length of the central shaft. The billet roll is of cylindrical shape in cross-section for use in handling flat sheets. The tongues and grooves of adjacent segments interfit closely and make parallel sliding contact over the length of the billet roll. The tight, sliding fit limits the use of the interfitting segments to cylindrical rolls.
U.S. Pat. No. 4,203,754 to Potier discloses a curved roll for conveying and shaping heat softened glass sheets that comprises a shaft having a curved portion, a rotary, flexible internally threaded tubular member slidably disposed about at least the curved portion of the shaft, a plurality of annular support means having external threading mating with the internal threading of the tubular member and sliding rings of graphite interposed between the curved portion of the shaft and the annular support means.
U.S. Pat. No. 4,226,608 to McKelvey discloses glass conveying and shaping apparatus comprising a series of horizontally spaced, flexible, conveying and shaping rolls that form a concave bed to receive softened glass sheets conveyed thereover. The opposite ends of the rolls are supported on end members whose positions are adjusted inwardly and angularly downward toward one another to apply end pressure to the opposite ends of the rolls to cause the rolls to assume predetermined concave elevational curvatures.
U.S. Pat. No. 4,311,509 to William D. Reader and Terry L. Wolfe, for APPARATUS FOR CONVEYING GLASS SHEETS, relates to curved conveyor rolls for conveying hot, flat glass sheets through a roll forming station and/or curved glass sheets into and through the cooling area of a glass sheet tempering apparatus. A conveyor comprising a plurality of said curved conveyor rolls defines a path of movement for the curved glass sheets through at least a portion of the roll forming station and/or the cooling area. The rolls extend transversely of said path and are spaced longitudinally along said path.
Each roll comprises a curved shaft having at least a portion thereof provided with an elevational shape conforming to the transverse shape of glass sheets transported thereover if located in the cooling area or the transverse shape to sag the hot glass sheets, if located in the roll forming station. A plurality of segments of essentially cylindrical configuration is mounted around said curved shaft in end to end relation with one another from one end segment at one end of said roll to another end segment at the other end of said roll. The segments intermediate the end segments have tongues extending from one axial side wall and grooves recessed within the opposite axial side wall. Tongues and grooves of adjacent segments form loose tongue in groove couplings. One of the end segments has tongues that extend to interfit loosely with grooves of its adjacent segment. The other end segment is recessed with grooves that loosely receive tongues extending from its adjacent segment. A spring mounted around the shaft insures positive interfitting between the tongues and grooves.
Means is provided to apply a torque to one of the end segments for transmission through said loose tongue and groove couplings to rotate said segments at equal rotational speeds so as to avoid scuffing the glass sheets transported thereover in the roll forming station of glass sheet shaping apparatus or the cooling area of glass sheet tempering apparatus. In addition, the loose tongue and groove couplings between adjacent segments permits a limited freedom of radial movement between said adjacent segments, whereby the segments, each comprising a hub surrounded by a collar, form essentially cylindrically-shaped segments of a segmented roll whose outer surface conforms to the shape of the curved shaft.
The segments are usable with shafts of different curvatures that are needed to produce different shapes. Only one set of segments is needed for many different production patterns.
Conveyor rolls of the Reader and Wolfe invention may be very closely spaced, if located in a roll forming station. Close roll spacing minimizes distortion of the hot glass due to sagging between adjacent rolls.
While the Reader and Wolfe rolls provide definite benefits in the handling of glass sheets during their transport over a wide temperature range, there are certain problems that require further improvements in the roll construction to overcome. These include the tendency of the springs that apply axial pressures against the end segments to weaken said end segments by marring their axial end surfaces that face the spring and to cause the rolls to drag at uncontrolled rates from roll to roll.